1. Field of the Invention
The present invention relates to an internal combustion engine device in which a catalyst for purifying an exhaust gas is provided in an exhaust gas passage of an internal combustion engine, and which includes air-fuel ratio sensors attached to the exhaust gas passage such that the sensors are positioned upstream and downstream of the catalyst, respectively, etc.
2. Description of the Related Art
In general, an exhaust gas emitted from an internal combustion engine which combusts fuel contains harmful substances. In recent years, emission regulations have become increasingly strict. Because of this, a two-wheeled vehicle, a four-wheeled vehicle, and other vehicles are each provided with a catalyst for purifying the exhaust gas by removing the harmful substances through an oxidation reaction and a reduction reaction, in an intermediate portion of an exhaust gas passage. To allow the exhaust gas to be efficiently oxidated and reduced by the action of the catalyst, it is required that an air-fuel ratio be an ideal air-fuel ratio in which the fuel and air are completely combusted, and that there is no excess oxygen. For example, in a case where the fuel is gasoline, the ideal air-fuel ratio is 14.6.
Japanese Laid-Open Patent Application Publication No. 2012-026306 discloses that air-fuel ratio sensors are attached to an exhaust gas passage of an internal combustion engine such that the sensors are positioned upstream and downstream of a catalyst provided in the exhaust gas passage, respectively, and a maximum oxygen storage capacity of the catalyst is estimated with reference to output values of these sensors. In this estimation of the oxygen storage capacity, it is necessary to provide an air-fuel ratio in a state in which the catalyst does not store (occlude) or release oxygen. The output values of the sensors, corresponding to the ideal air-fuel ratio, are provided off-line.